Trailer Control Valve With Integrated Trailer Supply

ABSTRACT

A trailer control valve for a tractor includes a body defining a supply port and first and second delivery ports. The supply port is configured for fluid communication with a fluid source on the tractor. The first and second delivery ports are configured for fluid communication with glad-hand connectors through which fluid is supplied from the tractor to a trailer for, respectively, releasing a parking brake and applying a service brake. The first delivery port is in fluid communication with the supply port. A relay valve is supported within the body and includes a valve member configured to move between positions preventing and permitting fluid communication between the supply port and the second delivery port. Pressure transducers in the body generate pressure signals indicative of fluid pressure at the delivery ports permitting detection of the presence of a trailer coupled to the tractor.

BACKGROUND OF THE INVENTION

a. Field of the Invention

This invention relates to a trailer control valve for a tractor-trailer. In particular, the invention relates to a trailer control valve that controls delivery of fluid to trailer brakes while providing protection for the tractor air supply.

b. Background Art

Conventional tractors include components for generating and storing pressurized fluid and for routing and delivering that fluid to wheel brakes on the tractor and any trailers coupled to the tractor in order to release parking brakes and apply service brakes. These components include various valves that control routing and delivery of fluid from a fluid source to the brakes. To control routing and delivery of fluid to the trailers, the tractor typically includes a relay valve as well as a tractor protection valve. The relay valve increases the volume of fluid, and therefore the speed, at which fluid is delivered to, and exhausted from, the wheel brakes on the trailer in order to eliminate lag times between the commanded and actual application and release of the trailer brakes. The tractor protection valve transmits pneumatic signals relating to operation of the trailer wheel brakes from the tractor to the trailer while also protecting the fluid supply for the tractor in the event of a break in the fluid connection between the tractor and trailer. Although conventional relay and tractor protection valves function well for their intended purpose, the use of separate relay and tractor protection valves increases the part count, cost and complexity of the fluid circuit on the tractor including the number of pneumatic connections.

The inventors herein have recognized a need for a trailer control valve for a tractor that will minimize and/or eliminate one or more of the above-identified deficiencies.

BRIEF SUMMARY OF THE INVENTION

This invention relates to a trailer control valve for a tractor-trailer. In particular, the invention relates to a trailer control valve that controls delivery of fluid to trailer brakes while providing protection for the tractor air supply.

A trailer control valve for a tractor in accordance with one embodiment includes a body defining a supply port and first and second delivery ports. The supply port is configured for fluid communication with a fluid source on the tractor. The first delivery port is in fluid communication with the supply port and configured for fluid communication with a first glad-hand connector through which fluid is supplied from the tractor to a trailer coupled to the tractor for releasing a parking brake on the trailer. The second delivery port is configured for fluid communication with a second glad-hand connector through which fluid is supplied from the tractor to the trailer for applying a service brake on the trailer. The valve further includes a relay valve supported within the body. The relay valve including a valve member configured to move between a first position preventing fluid communication between the supply port and the second delivery port and a second position permitting fluid communication between the supply port and the second delivery port.

A trailer control valve for a tractor in accordance with another embodiment includes a body defining a supply port and first and second delivery ports. The supply port is configured for fluid communication with a fluid source on the tractor. The first delivery port is in fluid communication with the supply port and configured for fluid communication with a first glad-hand connector through which fluid is supplied from the tractor to a trailer coupled to the tractor for releasing a parking brake on the trailer. The second delivery port is configured for fluid communication with a second glad-hand connector through which fluid is supplied from the tractor to the trailer for applying a service brake on the trailer. The valve further includes a relay valve supported within the body. The relay valve including a valve member configured to move between a first position preventing fluid communication between the supply port and the second delivery port and a second position permitting fluid communication between the supply port and the second delivery port. A first pressure sensor is supported within the body and configured to generate a first pressure signal indicative of fluid pressure at the first delivery port. A second pressure sensor is supported within the body and configured to generate a second pressure signal indicative of fluid pressure at the second delivery port.

A trailer control valve for a tractor in accordance with the present teachings represent an improvement as compared to valves used in conventional tractor fluid control circuits. In particular, the valve integrates functionality of a relay valve and a tractor protection valve to reduce part count, cost and complexity of the tractor fluid circuit including the number of pneumatic connections. In some embodiments, the trailer control valve also monitors the trailer supply and control fluid pressures to facilitate detection of the presence of trailers coupled to the tractor.

The foregoing and other aspects, features, details, utilities, and advantages of the present invention will be apparent from reading the following description and claims, and from reviewing the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic representation of system for controlling wheel brakes on a tractor and trailer in accordance with one embodiment of the present teachings.

FIGS. 2A-2B are perspective and side views of a trailer control valve of the system of FIG. 1.

FIG. 3 is a diagrammatic representation of the trailer control valve of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings wherein like reference numerals are used to identify identical components in the various views, FIG. 1 illustrates a vehicle 10 containing a tractor or power unit 12 and one or more trailers or towed units 14. Tractor 12 contains a power unit, such as an internal combustion engine, and steering and drive axles each of which support one or more wheels at either end. Trailers 14 are provided to store freight and are detachably coupled to tractor 12. Each trailer 14 is supported on one or more trailer axles, each of which may support one or more wheels at either end. Although vehicle 10 includes a single trailer 14 in the illustrated embodiment, it should be understood that the number of trailers 14 attached to tractor 12 of vehicle 10 may vary.

Vehicle 10 further includes a braking system 16 configured to brakes wheels on tractor 12 and trailer 14 in order to slow or stop movement of vehicle 10. System 16 may include components on both tractor 12 and trailer 14 that may be in fluid and/or electrical communication using conventional connectors between tractor 12 and trailer 14. Braking system 16 may include wheel brakes 18, a fluid circuit 20 that supplies fluid pressure to wheel brakes 16, various sensors (not shown, but including transmission speed sensors, wheel speed sensors, pressure sensors, a steer angle sensor, a yaw rate sensor, and load sensors) and a controller 22.

Wheel brakes 18 are configured to apply a braking force to the vehicle wheels. In the illustrated embodiment, brakes 18 comprise disc brakes in which a carrier supports brake pads on opposite sides of a rotor rotating with the wheel and a brake actuator causes, responsive to fluid pressure delivered by fluid circuit 20, movement of a caliper relative to the carrier to move the brake pads into and out of engagement with the rotor. It should be understood, however, that one or more of wheel brakes 18 may alternatively comprise drum brakes in which the brake actuator causes, responsive to fluid pressure delivered by fluid circuit 20, movement of a cam or piston to move one or more brake shoes into engagement with a braking surface in a brake drum rotating with the vehicle wheel. Each wheel brake 18 defines a service brake. At least some of wheels brake 18 further define a parking or emergency brake. In one conventional wheel brake 18, the brake actuator includes a spring that forces a pushrod in a first direction to move the caliper (disc brake) or cam/piston (drum brake) to apply the parking/emergency brake. Fluid pressure may be supplied to the actuator to overcome the force of the spring and cause movement of the pushrod in a second direction to release the parking/emergency brake. Fluid pressure may then applied to another portion of the actuator to again urge the pushrod in the first direction to apply the service brake.

Fluid circuit 20 generates fluid pressure within system 16 and controls the delivery of fluid pressure to the actuator of each wheel brake 18. Circuit 20 may include means for generating and storing pressurized fluid including a fluid source 24 and means for routing and delivering fluid pressure to wheel brakes 18 including fluid conduits 26, glad-hand connectors 28 between tractor 12 and trailer 14, and various valves including foot pedal valve 30, hand control valve 32, and a trailer control valve 34 in accordance with the present teachings. Although only valves 30, 32 and 34 are illustrated in FIG. 1, it should be understood that circuit 20 may further include other conventional valves including relay valves to increase the volume of fluid, and therefore the speed, at which fluid is delivered to, and exhausted from, wheel brakes 18 in order to eliminate lag times between the commanded and actual application and release of brakes 18, modulator valves that modulate fluid pressure delivered to wheel brakes 18 to implement anti-lock braking during a loss of traction, quick release valves to increase the speed at which fluid pressure is exhausted from wheel brakes 18 when brakes 18 are released, and a dash control valve that allows the vehicle operator to implement various functions including releasing parking brakes on tractor 12 or trailer 14 by supplying fluid pressure to oppose spring forces in the actuators for wheel brakes 18.

Fluid source 24 is provided to generate and store pressurized fluid. Fluid source 24 may include one or more fluid reservoirs for storing compressed fluid used in applying wheel brakes 18. Fluid source 24 may further include a compressor to draw in air and compress the air for delivery to the fluid reservoir or reservoirs. Fluid source 24 may further include one or more air dryers to collect and remove solid, liquid and vapor contaminants from pressurized fluid.

Fluid conduits 26 are used to transport fluid between fluid source 24, glad-hand connectors 28, valves 30, 32, 34 (and other valves not illustrated herein) and wheel brakes 18. Conduits 26 may be made from conventional metals and/or plastics and have connectors at either end configured to join the conduits 26 to corresponding components of circuit 20.

Glad-hand connectors 28 are used to transmit pressurized fluid from tractor 12 to trailer 14. One of connectors 28 is used to transmit fluid used to release the parking brake of each wheel brake 18 on trailer 14. The other connector 28 is used to transmit fluid used to apply the service brake of each wheel brake 18.

Foot pedal valve 30 is provided to allow controlled application of the brakes 18 by the vehicle operator by selectively releasing fluid pressure from fluid source 24. Valve 30 is supported within the cabin of tractor 12. Actuation of valve 30 by the vehicle operator allows fluid pressure to flow from fluid source 24 to various valves in fluid circuit 20 including trailer control valve 34. Valve 30 has fluid ports in fluid communication with fluid source 24 and trailer control valve 34.

Hand control valve 32 allows the vehicle operator to control the service brakes of the wheel brakes 18 on trailer 14 independently of the service brakes of the wheel brakes 18 on tractor 12. Valve 32 is supported within the cabin of tractor 12 and configured for actuation by hand. Actuation of valve 32 by the vehicle operator allows fluid pressure to flow from fluid source 24 to various valves in fluid circuit 20 involved in control of the wheel brakes 18 on trailer 14 including trailer control valve 34. Valve 32 therefore has fluid ports in fluid communication with fluid source 24 and trailer control valve 34.

Trailer control valve 34 transmits pneumatic signals relating to operation of the trailer wheel brakes 18 from the tractor 12 to the trailer 14. In accordance with one aspect of the present teachings, valve 34 also protects the fluid supply for tractor 12 in the event of a brake in the fluid connection between tractor 12 and trailer 14. In accordance with another aspect of the present teachings, valve 34 may also monitor the trailer supply and control fluid pressures to facilitate detection of the presence of trailers 14 coupled to the tractor 12. Referring to FIGS. 2A-B and 3, valve 34 includes a body 36 and a relay valve 38 and may further include double check valve 40, electronically controlled valves 42, 44, 46, and pressure sensors 48, 50.

Body 36 provides structural support for, and positions and orients, the other components of valve 34 including relay valve 38, double check valve 40, electronically controlled valves 42, 44, 46, and pressure sensors 48, 50. Body 36 protects these components against external objects and elements. Body 36 is also configured for mounting on tractor 12. Body 36 may be made from conventional metals or plastics. Body 36 defines a supply port 52, delivery ports 54, 56, and control ports 58, 60. Referring to FIG. 1, supply port 52 is configured for fluid communication with a fluid source on tractor 12 such as fluid source 24. Delivery port 54 is configured for fluid communication with a glad-hand connector 28 through which fluid is supplied from tractor 12 to trailer 14 to release the parking brakes in the wheel brakes 18 on trailer 14. Referring to FIG. 3, delivery port 54 is in fluid communication with supply port 52 such that fluid pressure at supply port 52 is routed directly to delivery port 54. Referring again to FIG. 1, delivery port 56 is configured for fluid communication with the other glad-hand connector 28 through which fluid may be supplied from tractor 12 to trailer 14 for application of the service brakes in the wheel brakes 18 on trailer 14. Control ports 58, 60 are configured for fluid communication with control valves in tractor 12. In particular, control port 58 may be configured for fluid communication with foot pedal valve 30 while control port 60 may be configured for fluid communication with hand control valve 32. Referring to FIGS. 2A-2B, body 36 further defines a terminal connector 62. Connector 62 defines a plurality of electrical terminals or pins for transmitting and/or receiving electrical signals. Valve 34 may communicate with controller 22 and other components and systems on vehicle 10 through connector 62 using a conventional vehicle communication bus such as a controller area network (CAN) (or another communication medium such as power line communication (PLC)). Referring to FIG. 3, in the illustrated embodiment, connector 62 defines eight terminals or pins with pin 64 providing power to valves 42, 44, 46 and pressure sensors 48, 50, pin 66 acting as a ground, pins 68, 70, 72 receiving control signals for valves 42, 44, 46, pins, 74, 76, transmitting pressure signals from pressure sensors 48, 50, and pin 78 providing a reference pressure sensor supply voltage for controller diagnostic purposes.

Referring to FIG. 3, relay valve 38 controls the delivery of fluid pressure from supply port 52 on body 36 to delivery port 56. Valve 38 includes a valve member 80 configured to move between a first position preventing fluid communication between supply port 52 and delivery port 56 and a second position permitting fluid communication between supply port 52 and delivery port 56. Valve 38 includes an inlet port 82, an outlet port 84 and a control port 86. Inlet port 82 is in fluid communication with supply port 52 of body 36. Outlet port 84 is in fluid communication with delivery port 56 of body 36. Control port 86 is configured for fluid communication with supply port 52 or one of control ports 58, 60 on body 36 depending on the positions of double check valve 40 and electronically controlled valves 42, 44, 46 as described in greater detail below. Control port 86 is therefore configured to receive pneumatic control signals from ports 52, 58, 60 that control movement of the valve member 80.

Double check valve 40 provides fluid from the highest pressure input among control ports 58, 60 to control port 86 of relay valve 38. In the absence of actuation of foot pedal valve 30 or hand control valve 32, fluid will not flow from either control port 58, 60 to control port 86 on relay valve 38 and (unless fluid flow is permitted from supply port 52 to control port 86 as discussed below), relay valve 38 will prevent fluid communication between supply port 52 and delivery port 56 on body 36. Actuation of one of pedal valve 30 or hand control valve 32 will create a pressure differential that opens check valve 40 and permits fluid flow from the corresponding control port 58, 60 to control port 86 on relay valve 38 (provided electronic control valve 42 is open as discussed below), causing valve member 80 to move to a position permitting fluid flow between inlet port 82 and outlet port 84 on relay valve 38 and, therefore, between supply port 52 and delivery port 56 on body 36 of valve 34. Double check valve 40 has inlet ports in fluid communication with control ports 58, 60 on body 36 and an outlet port in fluid communication with control port 86 of relay valve 38.

Electronically controlled valves 42, 44, 46 provide an alternative means to foot pedal valve 30 and hand control valve 32 for controlling relay valve 38. In the illustrated embodiment, valves 42, 44, 46 comprise solenoid valves. It should be understood, however, that valves 42, 44, 46 may assume other forms including motorized valves or piezo valves. Valve 42 is configured to control delivery of fluid pressure from control ports 58, 60 on body 36 to control port 86 on relay valve 38. Valves 44, 46 are configured to control delivery of fluid pressure from supply port 52 on body 36 to control port 86 on relay valve 38 (through restrictor 88). Valve 42 is normally open and valves 44, 46 are normally closed to permit fluid flow from control ports 58, 60 on body 36 to control port 86 on relay valve 38 upon actuation of foot pedal valve 30 or hand control valve 32. In certain circumstances, however, it may be desirable to actuate the service brakes on trailer 14 in the absence of actuation of foot pedal valve 30 or hand control valve 32 including in operator controlled electronic braking systems, advanced driver assistance systems (ADAS) such as collision avoidance systems, adaptive cruise control systems and platooning systems. In these circumstances, signals may be generated by controller 22 or another system or component on vehicle 10 and delivered to valves 42, 44, 46 through pins 68, 70, 72 of connector 62 to close valve 42 and open valves 44, 46 and modulate and deliver fluid pressure from supply port 52 of body 36 to control port 86 of relay valve 38.

Pressure sensors 48, 50 provide an indication of the fluid pressure at delivery ports 56, 54, respectively. Sensors 48, 50 are supported within body 36 of valve 34. Sensor 48 generates a pressure signal indicative of the fluid pressure at delivery port 56 while sensor 50 generates a pressure signal indicative of the fluid pressure at delivery port 54. In this manner, valve 34 allows monitoring of the fluid pressure in both fluid lines to trailer 14 (unlike conventional systems that measure pressure on only the control line) close to the physical connection with trailer 14. The measurement on both lines enables system 16 to provide accurate detection of the presence of trailer 14. Pressure sensors 48, 50 output pressure signals on pins 74, 76 of connector 62. Each pressure sensor 48, 50 is also in electrical communication with pin 78 providing a reference pressure value and a pin 66 tied to electrical ground.

Referring again to FIG. 1, controller 22 may be used to control the operation of various systems and components of vehicle 10. Controller 22 may, for example, be used to control braking and stability control systems in vehicle 10 by controlling the operation of various fluid control valves including relay valves and modulator valves. In accordance with one aspect of the present teachings, controller 22 may be provided to control the operation of trailer control valve 34. In accordance with another aspect, controller 22 may also detect the presence of a trailer 14 coupled to tractor 12 responsive to signals generated by valve 34 and, in particular, by pressure sensors 48, 50. Controller 22 may comprise a programmable microprocessor or microcontroller or may comprise an application specific integrated circuit (ASIC). Controller 22 may include a memory and a central processing unit (CPU). Controller 22 may also include an input/output (I/O) interface including a plurality of input/output pins or terminals through which the controller may receive a plurality of input signals and transmit a plurality of output signals. The input signals may include signals received from a variety of sources providing information about the operation of vehicle 10 including, for example, various sensors such as wheel speed sensors, lateral acceleration sensors, steer angle sensors, brake pressure sensors, vehicle load sensors, yaw rate sensors, tire pressure management sensors, and collision avoidance sensors (which may comprise, for example, RADAR devices, LIDAR devices or cameras). The input signals may also include inputs from user interfaces through which the vehicle operator can input data regarding the vehicle 10 and/or direct the operation of vehicle 10. In accordance with present teachings, the input signals may further include signals generated by pressure sensors 48, 50 in valve 34. The output signals may include signals transmitted to various vehicle control systems such as anti-lock braking and stability control systems and user interfaces on vehicle 10. In accordance with the present teachings, the output signals may further include signals generated to control electronically controlled valves 42, 44, 46 within valve 34. Controller 22 may communicate with other devices and systems within vehicle 10 over a conventional vehicle communication bus such as a controller area network (CAN) (or another communication medium such as power line communication (PLC)).

A trailer control valve 34 for a tractor 12 in accordance with the present teachings represent an improvement as compared to valves used in conventional tractor fluid control circuits. In particular, the valve 34 integrates functionality of a relay valve and a tractor protection valve to reduce part count, cost and complexity of the tractor fluid circuit 20 including the number of pneumatic connections. In some embodiments, the trailer control valve 34 also monitors the trailer supply and control fluid pressures to facilitate detection of the presence of trailers 14 coupled to the tractor 12.

While the invention has been shown and described with reference to one or more particular embodiments thereof, it will be understood by those of skill in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. 

What is claimed is:
 1. A trailer control valve for a tractor, comprising: a body defining a supply port and first and second delivery ports, the supply port configured for fluid communication with a fluid source on the tractor, the first delivery port in fluid communication with the supply port and configured for fluid communication with a first glad-hand connector through which fluid is supplied from the tractor to a trailer coupled to the tractor for releasing a parking brake on the trailer, the second delivery port configured for fluid communication with a second glad-hand connector through which fluid is supplied from the tractor to the trailer for applying a service brake on the trailer; and, a relay valve supported within the body, the relay valve including a valve member configured to move between a first position preventing fluid communication between the supply port and the second delivery port and a second position permitting fluid communication between the supply port and the second delivery port.
 2. The trailer control valve of claim 1 wherein the body includes a first control port configured for fluid communication with a control valve in the tractor and the relay valve includes an inlet port in fluid communication with the supply port, an outlet port in fluid communication with the second delivery port, and a control port configured for fluid communication with the first control port on the body and to receive a pneumatic control signal from the first control port that controls movement of the valve member between the first position and second position.
 3. The trailer control valve of claim 2 wherein the control valve comprises one of a foot pedal valve in the tractor and a hand control valve in the tractor.
 4. The trailer control valve of claim 3 wherein the body includes a second control port configured for fluid communication with another of the foot pedal valve and the hand control valve and the control port of the relay valve is configured for fluid communication with the second control port on the body and to receive a pneumatic control signal from the second control port that controls movement of the valve member between the first position and the second position.
 5. The trailer control valve of claim 4, further comprising a double check valve having a first inlet port in fluid communication with the first control port on the body, a second inlet port in fluid communication with the second control port on the body and an outlet port in fluid communication with the control port on the relay valve.
 6. The trailer control valve of claim 2, further comprising a first electronically controlled valve supported within the body, the first electronically controlled valve including a valve member configured to move in response to a first electric signal received on a first terminal on the body between a first position preventing fluid communication between the first control port of the body and the control port of the relay valve and a second position permitting fluid communication between the first control port of the body and the control port of the relay valve.
 7. The trailer control valve of claim 6, further comprising a second electronically controlled valve supported within the body, the second electronically controlled valve including a valve member configured to move in response to a second electric signal received on a second terminal on the body between a first position preventing fluid communication between the supply port of the body and the control port of the relay valve and a second position permitting fluid communication between the supply port of the body and the control port of the relay valve.
 8. The trailer control valve of claim 2, further comprising an electronically controlled valve supported within the body, the electronically controlled valve including a valve member configured to move in response to an electric signal received on a terminal on the body between a first position preventing fluid communication between the supply port of the body and the control port of the relay valve and a second position permitting fluid communication between the supply port of the body and the control port of the relay valve.
 9. A trailer control valve for a tractor, comprising: a body defining a supply port and first and second delivery ports, the supply port configured for fluid communication with a fluid source on the tractor, the first delivery port in fluid communication with the supply port and configured for fluid communication with a first glad-hand connector through which fluid is supplied from the tractor to a trailer coupled to the tractor for releasing a parking brake on the trailer, the second delivery port configured for fluid communication with a second glad-hand connector through which fluid is supplied from the tractor to the trailer for applying a service brake on the trailer; a relay valve supported within the body, the relay valve including a valve member configured to move between a first position preventing fluid communication between the supply port and the second delivery port and a second position permitting fluid communication between the supply port and the second delivery port; a first pressure sensor supported within the body and configured to generate a first pressure signal indicative of fluid pressure at the first delivery port; and, a second pressure sensor supported within the body and configured to generate a second pressure signal indicative of fluid pressure at the second delivery port.
 10. The trailer control valve of claim 9 wherein the body includes a first control port configured for fluid communication with a control valve in the tractor and the relay valve includes an inlet port in fluid communication with the supply port, an outlet port in fluid communication with the second delivery port, and a control port configured for fluid communication with the first control port on the body and to receive a pneumatic control signal from the first control port that controls movement of the valve member between the first position and second position.
 11. The trailer control valve of claim 10 wherein the control valve comprises one of a foot pedal valve in the tractor and a hand control valve in the tractor.
 12. The trailer control valve of claim 11 wherein the body includes a second control port configured for fluid communication with another of the foot pedal valve and the hand control valve and the control port of the relay valve is configured for fluid communication with the second control port on the body and to receive a pneumatic control signal from the second control port that controls movement of the valve member between the first position and the second position.
 13. The trailer control valve of claim 12, further comprising a double check valve having a first inlet port in fluid communication with the first control port on the body, a second inlet port in fluid communication with the second control port on the body and an outlet port in fluid communication with the control port on the relay valve.
 14. The trailer control valve of claim 10, further comprising a first electronically controlled valve supported within the body, the first electronically controlled valve including a valve member configured to move in response to a first electric signal received on a first terminal on the body between a first position preventing fluid communication between the first control port of the body and the control port of the relay valve and a second position permitting fluid communication between the first control port of the body and the control port of the relay valve.
 15. The trailer control valve of claim 14, further comprising a second electronically controlled valve supported within the body, the second electronically controlled valve including a valve member configured to move in response to a second electric signal received on a second terminal on the body between a first position preventing fluid communication between the supply port of the body and the control port of the relay valve and a second position permitting fluid communication between the supply port of the body and the control port of the relay valve.
 16. The trailer control valve of claim 10, further comprising an electronically controlled valve supported within the body, the electronically controlled valve including a valve member configured to move in response to an electric signal received on a terminal on the body between a first position preventing fluid communication between the supply port of the body and the control port of the relay valve and a second position permitting fluid communication between the supply port of the body and the control port of the relay valve. 